Take a walk on a large beach and it probably won’t be long before you come across some trash left behind. Old water bottles, garbage bags, straws and countless other varieties of plastic waste litter the world’s beaches and eventually end up in the ocean, where they break down over time. decades or even centuries. International coastal cleanup and ocean protection estimates that volunteers from 97 countries identified and removed around 4,000 tonnes of waste from beaches worldwide in 2021. For the most part, spotting all that trash still requires the naked eye and quite a bit of walking. But that could one day change thanks to a new satellite imaging technique developed by researchers at RMIT University in Australia.
The team developed a new tool that highlights unique spectral features in plastics. Armed with that knowledge, researchers could then accurately identify plastic objects on beaches and distinguish them from sand, water and vegetation. The researchers, whose work will be published in a upcoming issue of the magazine Marine Pollution BulletinAre there any hopeful coastal cleanup organizations that can use this new tool to speed up efforts to remove plastic from beaches, potentially reducing the amount of harmful plastic entering the oceans?
“This is incredibly exciting, because until now we have not had an instrument to detect plastics in coastal environments from space,” study co-author Mariela Soto-Berelov said in a statement.
Plastic waste is not just an ocean problem
Satellite images have been used for years to help scientists identify plastic floating in the ocean and in giant garbage patches like the Great Pacific Garbage Patch. This process works relatively well for identifying large pieces of plastic in the water, but is much less effective for detecting plastic on beaches. Coastal plastic often mixes with sand or is partially covered by sand, making spotting it much more difficult. And while plastic ending up in the ocean usually gets more attention, coastal waste can also have serious negative impacts on local wildlife.
“Plastic can be mistaken for food, larger animals become entangled and smaller animals, such as hermit crabs, become trapped in objects such as plastic containers,” lead study author Jenna Guffogg said in a statement.
These harmful effects are not limited to life on beaches either. If plastics are not removed, they can often be sucked into the ocean, where they are slowly broken down into smaller micro- and nano-plastics. These small plastics are then consumed by fish and work their way up the food chain. Some researchers believe this cycle may even contribute to an increase in the number of cases of microplastics detected in humans. Researchers fear this could lead to hormone disruption and worsening reproductive health. The full extent of the effects of microplastics on human health is still not fully known.
Finding plastic in sandbag
That’s where the new plastic detection system comes into the picture. The RMIT created a new “spectral index” that looks for patterns of reflected light coming from plastic. Plastics in particular have special characteristics in the shortwave infrared (SWIR) electromagnetic spectrum that are not present in sand or other organic waste. The index they created, the Beached Plastic Debris Index (BPDI), essentially works as a filter that can be applied to images of beaches captured by satellite. In this case, those images were created by Worldview 3–a satellite at an altitude of 617 kilometers above the Earth’s surface.
To test their new tool, the researchers went to a recycling facility and collected various types of plastic waste that would likely be found on a beach. Many of the objects were fragments of larger pieces of trash. Some had also had their colors faded from UV exposure, something that would likely happen if trash littered beaches. Ultimately, they came up with fourteen different plastic targets of approximately two square meters in size. These were placed 3.7 meters apart on a beach in Victoria, Australia.
Once the plastic was in place, the satellite flew far above our heads and took a series of photos. Researchers applied their index to the images and compared them with three other already developed instruments intended for detecting plastics: two for plastics on land and one for objects floating in the ocean. The BPDI index far outperformed the other three indices in terms of accuracy. The other three generally had difficulty identifying plastics and in some cases even incorrectly identified shadows as waste. Still, the BPDI index was not perfect. In particular, the study notes that it struggled to identify translucent polymers such as plastic water bottles and bags.
Looking to the future, the researchers want to move these findings out of limited testing environments and into the real world. That could mean working with other organizations that specialize in coastal plastic removal to use their satellite imaging technology. Time is of the essence. Recently Studies suggest the amount of plastic ending up in the oceans does not decrease and can increase by 4% per year.
“We want to work with organizations on the next step of this investigation,” Soto-Berelov said. “This is an opportunity to help us protect vulnerable beaches from plastic waste.”
